Bile Acids Total

Indications:

Changes in serum bile acids are seen in quite mild liver disturbances. The test may be used with other parameters such as serum glutathione-S-transferase (GST) and gamma-glutamyl transferase (GGT) activities to provide a very sensitive test of liver function. Bile acid measurement is not indicated in subjects who are overtly cholestatic (jaundice with high serum bilirubin) as bile acids do not provide further information on hepatobiliary function in this setting.

Elevations in circulating bile salts can be a cause of pruritis, typically on the palms of the hands and the soles of the feet. The commonly accepted clinical indication for making this measurement is in the investigation of obstructive cholestasis in pregnancy [3].

Bile salts are, however, far more than gastro-intestinal detergents [4]; they are required for cholesterol and fat-soluble vitamin absorption, as well as conferring resistance to the overgrowth of pathogenic intestinal bacteria. They are required for the activation of enterokinase (an enzyme released by the enterocytes as food passes into the duodenum which activates the proteolytic enzymes secreted by the pancreas). Bile salts have also been shown to enhance glycaemic control and energy expenditure via cell signalling pathways. It is therefore interesting to read current research which suggests that there is a blunted bile salt response to feeding, with increased bile salt turnover, in obese subjects. These changes could result in more efficient absorption of dietary fat in such individuals [5].

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Serum total bile acids may therefore provide additional information in the investigation of a number of disturbances to the physiological functions described above.

Interpretation

The test is usually performed on a fasting sample, with normal fasting serum total bile acids being less than 6.4 ?moles/L. The measurement of bile acids in paired (fasting and 2 hour post-prandial) samples will increase the test sensitivity; two-hour post-prandial bile acid concentrations of > 20 Ámol/L are suggestive of hepatobiliary disease.

Other variables, independent of hepatobiliary function, may affect serum bile acid concentrations:?1. Inadequate fasting or decreased gastrointestinal transit time can increase fasting bile acid concentrations, which can, in some cases, be higher than the postprandial bile acid concentration.2. Prolonged fasting, intestinal malabsorption or increased transit time through the bowel (e.g. diarrhoea) can lower bile acid concentrations and hence decrease the sensitivity of the test as an indicator of hepatobiliary disease.